Labour's triumph came over as the clear message from Glasgow North East despite the problems of measuring it.
The new constituency was created under boundary changes in 2005 since when its only MP has been Michael Martin who ran as the Speaker - not a party candidate - in the last election with no Labour, Tory or Liberal Democrat runners.
This means no exact swing comparisons can be made.
In fact 4,036 people backed the Socialist Labour Party runner in 2005 - presumably because most of them were searching for Labour's name on the ballot paper.
In yesterday's by-election the SLP got just 47 votes.
Some guidance can be offered by last June's European Parliament voting in the constituency.
Labour then had a 16.3 per cent lead over SNP which has now jumped to 39.4 per cent - a swing of 11.5 per cent.
This does not take the party all the way back to 2005 General Election support but probably close to what it achieved at last year's Glenrothes contest when there was a switch of less than 5 per cent to the nationalists since 2005.
If repeated at the General Election it would give the SNP just one extra Westminster seat - at Ochil and Perthshire South.
But past by-elections suggest there could not be any guarantee of even that.
David Kerr, Glasgow North East's SNP candidate, stood at the December 2000 Falkirk West by-election when he missed a gain by only 705 votes on a huge swing.
In the General Election six months later the party ended up losing a Westminster seat at Galloway and Upper Nithsdale.Reuse content